I think ez061111 point is you don't need either and your system will run better without.

I don't normally run any antivirus and haven't since I started using a Mac. However I have started using a simple scanner which I update and run every month or so just to be sure I'm not going to inadvertently pass something to windows friends or to my work machine also running windows.

This isn't a background scanner and only runs when I start it so there is no overhead to having it installed.